Welding past, present and future. David LeBlanc will combine features from Oak Ridge’s 1960s molten salt reactor with the SmAHTR concept, to make his own “Integral Molten Salt Reactor.” That’s not LeBlanc above. It’s a welder finishing up the Oak Ridge MSR over 40 years ago.

The more I watch developments in the molten salt reactor field, the more impressed I am by the variety of innovative approaches.

While every molten salt reactor project I’ve encountered traces its inspiration and probably its basic design to the 1960s Oak Ridge National Laboratory project in Tennessee, the number of modifications that different labs are pursuing is starting to resemble the type of competitive differentiation that defines a free market.

Before I get too carried away, let me acknowledge that MSRs are a long way from the market (although with the right breaks, not as long as some would believe). Thus, it’s admittedly premature to compare them to the thriving technological leapfrogging of, say, the automobile or information technology industries.

But MSR companies nevertheless are in the early stages of trying to one-up each other as they all chase the general goal of building a reactor that runs on liquid fuel rather than on conventional solid fuel, and that provides a host of improvements in safety, efficiency and long-lived waste reduction.

The most recent case in point comes from the newest of the statups: Terrestrial Energy Inc., based in Ottawa Canada, and run by co-founder, president and chief technology officer David LeBlanc.

Dr. LeBlanc is an MSR expert who in January wrote a guest blog here in which he pointed out among other things that it would be in the best interest of the MSR industry to keep designs as simple as possible in order to stand a chance of commercializing within a reasonable time frame.

That advice struck me as sensible, so I made a point of following up with LeBlanc, who incorporated Terrestrial in late 2012 after several years of running an MSR intellectual property company called Ottawa Valley Research Associates.

We spoke by Skype last week, when LeBlanc explained the pragmatic reasoning behind his simplicity push, noting that, “You cannot underestimate the cost of nuclear R&D.”

BURN DON’T BREED

He outlined his plan for simplicity. In keeping with the theme, let me attempt to keep it simple: Terrestrial Energy is departing from the original Oak Ridge scheme that called for a two-fluid molten salt reactor that would breed its own fuel. Instead, Terrestrial’s design calls for a single fluid reactor that would “burn” rather than breed. In the nuclear lexicon, LeBlanc’s reactor is known as a “burner” or a “converter”, not a “breeder.”

While a two-fluid breeder would be the “Ferrari” of MSRs, the world cannot afford to wait for its development, given the desperate need for CO2-free energy sources such as MSRs, notes LeBlanc.

Dual fluid breeder MSRs face a number of extra challenges that will prolong their development beyond that of a single fluid MSR. Among them:

The infamous “plumbing problem” that vexed Oak Ridge. In a two-fluid design, one fluid continuously breeds fuel, feeding it into another fluid where the nuclear reaction takes place. The pipes and materials that house and separate the fluids are subject to damaging wear and tear.

Dual fluid breeders require constant removal of fission products, which are the short-lived radioactive waste products of a nuclear reaction (different from the long-lived “actinide” wastes like plutonium) “That requires a lot of R&D and a lot of capital to develop,” notes LeBlanc, who points out that in the 1960s, Oak Ridge had planned to remove fission products on a 10-day cycle by removing a tenth of the salt each day.

Compared to a breeder MSR, a burner based on denatured uranium has the obvious disadvantage of not running forever on its bred fuel. LeBlanc downplays that, noting a once-through cycle can last for up to 30 years in a single fluid MSR. In addition, the actinides – which are much less than in conventional reactor waste – could potentially be removed at that point and recycled into the next fuel batch, minimizing long-term waste storage needs.

Packing a punch. LeBlanc’s high power density design means that his IMSR can be smaller than other modular reactors. Above, he compares a 25 MWe and 300 MWe version of the IMSR to the SmAHTR design, and to more conventional modular reactors from Nuscale and Babcock & Wilcox. He borrows from a famous VW ad slogan. Spot the Beetle – it’s to scale.

Those 30 years, though, would require annual top-ups of uranium. But as LeBlanc points out, the amount would be only about one sixth of the uranium requirements for today’s conventional solid fuel reactors.

Toward the end of its molten salt reactor days, Oak Ridge designed and built a single fluid MSR to run on denatured uranium, along with thorium, called a DMSR.

GET SMAHT

Terrestrial Energy is drawing on that design, but is combining it with principles borrowed from another technology called SmAHTR, for Small Modular Advanced High Temperature Reactor.

The 50-megawatt (electric) SmAHTR is a conceptual innovation at Oak Ridge. It is a small version of the liquid cooled 1500 MWe AHTR – on which Oak Ridge is collaborating with China – that places the heat exchange inside the reactor vessel.

SmAHTR and AHTR introduce liquid cooling (molten salts) to high temperature next generation solid fuel reactors such as those that use TRISO fuel – pebble bed reactors – and those that use prismatic blocks where the fuel is embedded in graphite blocks that serve as the moderator. Those reactor designs have in the past typically used helium gas as a coolant, which presents various mechanical difficulties and requires high pressure.

LeBlanc believes that by switching the fuel into the molten salt, it offers many benefits of liquid fuel while retaining innovative features of the SmAHTR design. One such benefit: The reactor generates heat directly in the liquid fuel, which permits higher power density operation. Placing the heat exchanger inside the reactor vessel rather than outside – as with some other MSRs – helps.

That, in turn, will allow Terrestrial to build smaller but equally powerful reactors compared to other small modular manufacturers that are using more conventional solid fuel, water-cooled designs, such as Babcock & Wilcox (see diagram above).

NAME THAT REACTOR

Not to be outdone on the nomenclature front, and in keeping with the MSR industry’s nascent differentiation trend, Terrestrial gives its reactor a unique name: the Integral Molten Salt Reactor, or IMSR.

The IMSR will also include patent pending innovations, on which LeBlanc declines to publicly elaborate.

Another IMSR feature: It will use a core of graphite moderator slabs between which the fuel flows which LeBlanc says, “allows other advantages like tricks to limit the amount of neutrons reaching the vessel wall.” This addresses a problem that developers of liquid fuel fast reactors will find difficult to crack, he notes.

With the right combination of power density and core design Terrestrial could build the IMSR with upwards of six times the electrical output of the same size vessel as SmAHTR. It would require replacing the graphite core every four years. The fuel would reside temporarily in a holding tank during the core swap. That marks an improvement over the SmAHTR concept, which requires a swap of the solid fuel core every four years.

LeBlanc envisions IMSR reactor sizes ranging from 25 MWe to 300 MWe.

As with other MSR startups, such as the Japanese single fluid company Thorium Tech Solution, LeBlanc is undecided on exactly what salt he’ll use. While FLiBe salt (lithium fluoride and beryllium fluoride) is commonly associated with dual fluid MSRs, its lithium isotope is problematic, for reasons I’ll examine in a subsequent blog.

LeBlanc says he is considering alternatives including sodium based salts.

In the long run, he has not ruled out a breeder design or thorium fuel, but for now, he’s focused on the single fluid uranium reactor.

I read this and I think, I hope this results in fulfilling the promise of LFTR, cheap, clean, non proliferating, carbon free, energy to replace the expensive, dirty, carbon emitting sources of energy, not to mention the promise of prosperity, always in the past dependent on cheap energy!

It’s gratifying to see SmAHTR contribute to the dialogue concerning fluoride salt-cooled, and fluoride salt fueled reactor development. Our goal with SmAHTR was to “move the needle” by integrating lessons learned from MSR technology and MSR concept development with the realities of modern reactor develop environment. I remain convinced that a “relatively low temperature” (relative to fluoride salt capabilities) salt-cooled concept is the best evolutionary starting position for modern MSR development.

Sherrell Greene
SmAHTR Concept Development Lead and former Director of Nuclear Technology Programs at Oak Ridge National Laboratory

Great to hear from you Sherrell and thanks so much to you and your group for the work on SmAHTR, sad to see the DOE not funding that route more.

You added a mysterious quote there about lower temperatures that fluorides? Are you thinking chloride salt coolants? Going the faster spectrum route has many new challenges as well I would think, maybe hard to class as a simple first step (but I’m only guessing of course).

Anyhow, my viewpoint, and expressed well by David Holcomb (current salt cooled lead at ORNL) in his concluding remarks at the recent Molten Salt conference in India was salt cooled (FHR) and salt fueled (MSR) can certainly be parallel development, not necessarily one first, then the other. With the enormous market potential and critical need of these various systems there is certainly room for cooled and fueled as well as burner or breeder at the same time. And, as we all often point out, 95% of needed R&D is going to overlap anyhow (I’d like a canned pump if you don’t mind….)

Dear David & Sherrell,
Great to hear the above details from you gents!
Not happy to hear however that DoE has de-funded ‘SMAHT’ technology in the US (but still asst’g China, cérto?).
Is the loss of funds due to “sequestration” or what, and how is good Jess G. faring ??

It’s impressive how the article jumps from admission that MSRs are a long way from the market to a flight of fantasy about what is going to happen with imaginary nuke technology. We can achieve so much with imaginary nuke technology.

It’s important to note that the diagram comparing the sizes of SMRs is misleading: Both mPower and NuScale designs INCLUDE the steam generator inside the tall vessel.
The IMSR and SmAHTR do not: The heat exchangers inside the vessel simply transfer the heat outside the reactor vessel to a tertiary loop which presumably includes a steam generator, or possibly an SCW turbine.
Also, the mPower and NuScale units sit inside a deep pool of water, for a nice simple system of shielding & cooling.
The much hotter IMSR and SmAHTR cannot be put in a pool of water: Instead they are typically installed in a “hot cell” which is a relatively complex enclosure filled with inert gas, with fancy walls, floor and ceiling comprised of a layer of refractory material, gas or liquid cooling pipes or ducts below that, and finally a thick layer of concrete (only the last is comparable to the water pool wall). Same for the fuel salt storage tank(s).

A fair size comparison should include both the power conversion equipment (water HX & SG if any) as well as the hot cell(s) & associated equipment.

Yes, that is true steam generators (or transfer to He or CO2 if that is the preference) are not show for SmAHTR or IMSR. For steam at least they are very compact only would only increase the overall volume by a very small fraction if shown. As well, since both salt cooled and salt cooled systems can produce high temperature heat, there may be more market just for the heat, not to make steam or electricity.
As for showing a full building, plant comparison etc. Please give us some time.

Not so fast, because much more important than overall volume is the volume of the hardware to be pressed into containment. Another point is that the IMSR could drive He or CO2 cycle turbines, potentially making the rest of the plant even more compact than nuclear island.

David,
I agree development of small integral MSRs (IMSRs) and fluoride salt cooled reactors (FHRs such as SmAHTR) could proceed in parallel. But I’m torn. There are many “urban myths and legends” still floating around about the MSRE experience (both overly-optimistic and overly-pessimistic in my view). Licensing a fluid-fueled reactor (especially if the fuel circulates outside the reactor vessel) is going to be a real challenge. Your IMSR concept does much to address these concerns, but there are residual fuel chemistry / material worries that will probably slow down licensing of any MSR. Going with an integral FHR design MIGHT provide a more evolutionary (and therefore more palatable) approach to addressing these issues. In both cases (IMSR and IFHR) the concepts lend themselves well to small distributed process heat and power (presuming the thermal-to-electric conversion system issues can be solved) applications. Both concepts face many technical (an non-technical) challenges on the path to becoming a reality. But in my view, both approaches potentially provide such benefits as to warrant serious exploration. Nuff for now. Have to run to Church. Cheers!

Well put. I’d just mention that there is still innovation I have not yet disclosed that II feel will make a significant improvement on some of the many great challenges you’ve reminded us of. And, as is often the case there may be aspects transferable to salt cooled (FHR) as well. I look forward to discussing this with you in the future.

The on-going TMSR project at Shanghai CAS is pursuing the two-prong approach. The near-term one being the molten salt cooled pebble-bed reactor and longer term one being the two-loop MSR with on-line U-233 breeding and fission-product extraction. The HTR-10 project has demonstrated the inherent safety capability of helium-cooled pebble-bed reactor via a series of transient experiments (Blower shut-off without scram; All rod run-out; Total load reject, etc.). A commercial demo pair HTR-PM is currently under construction to be on-grid by 2017 at a budget cost of ~$2000 per kWe. If successful, 36 HTR-PM modules capable of 3.8 GWe will be constructed at the same site in Rongcheng, Shangdong. The initial effort of TMSR project is to upgrade the HTR-PM performance via conversion of the helium cooling into molten salt cooling. This seemingly simple task will take at least ten years to complete. In the meantime, the HTR-PM could by itself to be a highly successful power generator to compete with coal-fired power plants to help with the war on global warming.

RE: comparison of reactor sizes–Please also note that the NuScale rendering includes the outer containment (note the separate pressure vessel within), while the mPower rendering is of the pressure vessel alone. This explains the disparate power densities of apparently similar-sized PWRs.

I think the most apples-to-apples comparison shown is between the mPower pressure vessel (160 MWe) and the IMSR 300 (300 MWe). You can go to mPower’s website and look at a rendering of the full installation to get a feel for the footprint. Future generations will look back at PWRs the way we look at Zeppelin’s compared to today’s 747s.

Denatured, single-fluid, burner, and as simple as possibly achievable really looks like the way to go for the shortest path to industrialization.

Looking at the drawing there are still many things left to the imagination.
A question I suspect any LFTR advocate will ask is “where are the freeze plug and dump tank?”. There won’t be a need for any of those two if a passive decay heat removal system similar to the one proposed for the SmAHTR is used.
Will preferential plating out of fission products on easily replaced parts be used in the IMSR?
I wonder about the integration of the off-gas system and the instrumentation with neutron flux, temperature and pH sensors, especially their locations.
I also wonder how the salt will get its annual uranium (fluoride?) makeup. Online through a refueling port? Heavier intervention accompanied with downtime?

Excellent questions. I’ve discussed this a little on another site and we will be adding more details to our website in the coming weeks (but much will remain undisclosed).

FIrst is the obvious issue of decay heat removal. Yes, the default would be to add in a freeze plug at the bottom to allow passive draining to a dump tanks. However, there are many interest other options under investigation for pulling out the decay heat more directly, either by methods through the vessel wall or even using the SmAHTR approach of extra heat exchangers built in and operating by natural circulation. This area will obviously be one we will spend a great deal of effort to find the most practical approach but we appear to have many good options.

Another perhaps obvious area is the need to add makeup fuel (not really refueling, just topping up) and to of course sampling for salt chemistry etc. This can be handled by quite modest penetrations into the vessel.

Getting too deep into these and other questions though starts to get into proprietary realms.

The answer to 400 p.p.m. of CO2 in the global atmosphere (and rising) as measured by the earth station on Hawaii, is to phase out fossil fuel burning as a matter of most urgent priority. An answer to using Thorium MSR technology for this purpose, is to interest one of the growing band of billionaires to fund a private initiative. This initiative would be to mass produce small scale electricity generating units for commercial sale. The global energy market is $3 trillion per annum, which Thorium MSR technology would capture a significant part of. Time for talking is over, time for action is now.

In this context, I believe carbon dioxide is a ‘red herring.’ The carbon dioxide green house effect is a is a saturated, narrow-band process that is governed by a law of diminishing effect. The amount of CO2 added so far is equivalent to the difference between putting four instead of three coats of red paint on a barn.

The raw calculated effect (neglecting any hypothetical climatic feedback enhancement or diminution) is on the order one degree C for each complete doubling of the amount in the atmosphere. Thus beginning with a base concentration of 280 PPM CO2 before the exploitation of petroleum, a concentration of 560 PPM would be required to produce a raw increase of one degree C and 1120 PPM for two degrees.

While some IPCC models are based on assume feedback enhanced sensitivities as high as 3.3 degrees C per doubling, the data doesn’t seem to be supporting this assumption as a general rule. According to the UK Met office and the Hadley Climate Research Unit, global temperatures have increased, on average, about 0.8 degrees C since 1920. As the CO2 concentration has gone up by a factor of about the square root of two (a half doubling) in that time, it seems difficult to support a sensitivity greater than 1.6 degrees per doubling assuming one could prove that land-clearing, raw-energy-use, all other anthropogenic pollutants, and natural climate cycles have played no part in increasing the Earth’s average temperature over the period.

I believe the more important issue is the impending progressively increasing cost of chemical energy as the naturally concentrated resources, which took millions of years to form, are depleted, one by one.

“In this context, I believe carbon dioxide is a ‘red herring.’ The carbon dioxide green house effect is a is a saturated, narrow-band process that is governed by a law of diminishing effect.”

I think the above notion is an error that was resolved quite some time ago within climate science (article hosted at the American Institute of Physics):

“Then why pay attention at all to CO2, when water was far more abundant? Although Arrhenius understood the answer intuitively, it would take a century for it to be explained in thoroughly straightforward language and confirmed as a central feature of even the most elaborate computer models. The answer, in brief, is that the Earth is a wet planet. Water cycles in and out of the air, oceans, and soils in a matter of days, exquisitely sensitive to fluctuations in temperature. By contrast CO2 (and other, less important greenhouse gases like methane) linger in the atmosphere for centuries. Thus it is these gases that act as the “control knob” that sets the level of water vapor. If all the CO2 were somehow removed, the temperature at first would fall only a little. But then less water would evaporate into the air, and some would fall as rain. With less water vapor (and also less clouds retaining heat at night) the air would cool further, bringing more rain… and then snow. Within weeks, the air would be entirely dry and the Earth would settle into the frozen state that Fourier had calculated for a planet with no greenhouse gases.”

Capital looks for a market. I suggest the markets are NOT existing power companies. Instead, the market are high electricity consuming manufacturers, small and medium sized cities, large residential developments, business/industrial park developers, economic development departments of counties/cities. All of the foregoing are highly competitive markets who would seriously consider how low cost, uninterrupted power supply would provide/increase their competitive advantage in their respective markets. Let the target market have substantial impact on the “refueling”, maintenance, etc. aspect of the design. A 30 year guarantee of uninterrupted power may be preferable to an end user versus a higher efficiency source that requires 5 year significant maintenance. The installed purchase price is the 4th hurdle. The 1st hurdle is demonstrable safety. The 2nd is regulatory which can be overcome with the political clout and capital of the intended class of end users demanding the approval of the product. The 3rd hurdle is an accurate budget for maintenance/replacement although assuming that technology advancements will bring replacement costs down. Also, a leasing business model should be considered to overcome some regulatory issues over control/security of nuclear material. Science creates the opportunity for a product, but the degree and ease to which the product can be used effectively and efficiently by the ultimate customer determines whether any given technology will find success in the real world.

I agree with EMbar. The CO2 is a red herring. While I was an adjunct professor Peking University three years ago, my colleague, Prof. Qian from the Atmospheric Physics Dept, showed me his team’s research result. I recalled the following conclusions. (1) Greenhouse effect is mostly from water molecule in air and the CO2 contribution is less than 10%; (2) The increase in the atmospheric CO2 in ppm from 280 to 385 in 2010 has only marginal effect on the global temperature. (3) Prof. Qian’s PKU research group’s predictive model using more historic data suggests that the global temperature will not go beyond the 2 deg C. Actually, his paper predicted the rise is to slow down and reverse direction by mid-century. His model seems to be working so far.
EMbar’s belief of the rapid depleting fossil resource (coal, oil and NG) is indisputable. What concerns me more is the near-term health effects of burning these hydrocarbon fuels, not just the PM2.5 particulates but the discharge over a million tons of uranium into the atmosphere since last century. We are still spewing 20,000 tons of uranium a year. These uranium will quickly settle down on the surface of the Earth and become the ready source of radon gas, more specifically the Rn-222 which is the most lethal isotope because it is killing about 22,000 American every year according to the US Surgeon General. I won’t be surprised that quite a few of these RN-222 caused deaths are attributable to the increased uranium on the top soil. So this is just one more good motivation to speed up the development of an inherent-safe, economical and sustainable thorium-based molten salt reactor (TMSR). The fully matured TMSR might take too long to get to the deployment phase. The Mother Earth can’t wait that long. I favor the interim approach by CAS/SINAP of combining the high-temperature pebble-bed reactor technology such as the commercial demo HTR-PM being built in China with Flibe coolant used in MSRE at ORNL half a century ago. The last I heard is that the pilot experimental unit will be ready for criticality test in 2017. The same year the twin 210 MWe HTR-PM will be up and running.

I believe the IMSR is currently the most promissing new nuclear design.
1 – Keep the usage of molten salt coolant, but give up everything that isn’t essential to get an MSR to the market very quickly (7 years is a flash for nuclear technology)
2 – Keep the molten fuel and the 1/6th fuel yearly fuel makeup promisses the reactor will offer much lower O&M costs than any other nuclear reactor in operation. No solid fuel fabrication costs. Using just 1/6th new fuel every year, plus the ability to recycle the salt and the fuel once the reactor is replaced (using pyro reprocessing) helps O&M costs greatly too. The reactor is far less sensitive to any rise in Uranium costs in the future (although it looks like we can double uranium consumption with very little increase in uranium costs today, we just don’t have nearly). Replacing a large number of old LWR/BWR with IMSRs would allow for doubling energy output with half the uranium consumption
3 – While the IMSR has no core reprocessing capabilities using an external reprocessing facility every 5-10 years reduces makeup fuel even further
4 – Recycling the core fluid keeps almost all transuranics in the reactor until fully fissioned, except for a tiny reprocessing loss of 0.1% (standard in pyro reprocessing studies), this means that IMSR + infrequent pyro reprocessing should reduce SNF production by two orders of magnitude over existing reactors. The interesting variable is how the makeup fuel could be reactor grade plutonium + other actinides instead of LEU. This would greatly reduce the volume of make up fuel inserted yearly in the reactor and greatly increase the total burnup of the reactor until decommissioning.
PS: Don’t take me too seriously. I don’t have a nuclear degree. Any corrections are greatly appreciated.

I have a dual masters degree in structural & mechanical engineering. I have 22 years commercial and industrial plumbing, an a member of local union # 246.

I have been reading about MSR’s the problem with deteriorating piping from the salts, the plumbing so to speak could be lined with Pyrex, glass piping with a stainless jacket. There would not be any way to protect the heat exchangers from corrosion, but they could be coupled with dual valves on either end for a quicker way to change the parts out that do corrode to the point of needing replacement.

Another question.. Since the MSR’s are low pressure, could a person build one that is.. say 2.5kw – 5kw?

I would like to say smarter yet is Cavitation of FLiBe in an ultra sound generated Thorium Decay Plasma harvested by direct conversion of plasma to electric current in confined TEMHD in layered molten metal and salt configuration. An adjunct to molten metal storage battery technology with advantage of lower cost and higher efficiency by direct plasma to electric current conversion.

Containment vessel design would benefit from Graphite/Ceramic braze bonded to Hastelloy-N with a simple shield blanket of saturated Boric Acid. Operating temperature at 500 C if Calcium/Magnesium alloy is used in the TEMHD that could be aided with addition of samarium/cobalt beads in the mix.

So many possibilities on the table. I have collected 62 new energy production and storage effects and technologies over last eight years. They may not all grow to maturity, but several of them are in the home stretch. Several of these technologies would fit nicely under the hood of a Toyota, and power it for perhaps years on end. They are the product of Condensed Matter Physics, Nanotechnology and the development of Metamaterials. And if you want to go really far out consider NASA’s recent launch of an EmDrive space craft.

We stand at the dawn of a new Age of and for Mankind. Clean, Cheap, Safe, and extremely Scalable energy production and storage are within out grasp. Let us not fumble the ball as we have several times in the past.

I warmly welcome the Alvin Weinberg Foundation’s evidence-based approach to the energy debate, and enthusiastically support its mission to raise awareness of next-generation nuclear energy amongst NGOs and the general public.